In Project 1 we will identify and characterize new mutations in tyrosine kinases, and related signal transduction proteins, in ALL using novel genome-wide screening strategies. We have already identified mutations in tyrsoine kinases that demonstrate the validity of this approach. We will characterize mutant kinases in various models of transformation, and will develop small molecule inhibitors of these kinases in preclinical development. During the prior funding period, Dr. Gilliland and Dr. Armstrong, the coinvestigators on this proposal, developed extensive data demonstrating that ALL, like other human cancers, is the consequence of multiple mutations. Furthermore, they have identified several uncommon, but highly informative, examples that implicate mutant, constitutively activated tyrosine kinases in pathogenesis of ALL, including ABL gene rearrangements and FLT3 activating mutations. These data suggest that sensitive genome-wide screens for similar mutations in tyrosine kinases will provide additional insight into molecular pathophysiology disease, and will identify new targets for therapeutic intervention. Indeed, with the discovery of FLT3 mutations in a subset of cases of MLL rearranged infant leukemias, and of the NUP214- ABL fusion in a subset of T-ALL, targets have been identified that are suitable for immediate clinical translation in Project 6 with FLT3 inhibitors and the ABL inhibitor, imatinib. The Specific Aims are to 1. perform genome-wide screens for activating mutations in the kinome across the spectrum of pediatric leukemias. The screens will include (a) high-throughput DNA sequencing of the kinome and (b) high-density oligonucleotide array comparative genomic hybridization to screen for 5' activating deletions in the tyrosine kinome. 2. validate novel mutations by re-sequencing, and sensitive cell-based assays for kinase activation, and 3. develop and test small molecule inhibitors of mutant activated kinases. Project 1 will interact extensively with Projects 2 and 3 to test novel mutations mutations as cooperating events in TEL-AML1+ B-ALL, and in T-ALL, respectively;Project 4 to assess impact of kinase mutations on gene expression signatures;Project 5 to assess impact of these mutations on glucocorticoid induced apoptosis;and with Project 6 to test mutant kinases as targets for clinical therapy. As proof-of-principle for this approach, noted above, we have recently identified a novel NUP214-ABL fusion in a signfiicant proportion of cases of T-ALL due to a novel episomal fusion mechanisms that is a target for imatinib therapy Project 6, and activating mutations in FLT3 in MLL rearranged infant leukemias that are candidates for therapy with FLT3 inhibitors.